Did you make a decision yet?
The MR-1 is almost in a class by itself at the moment. I'll compare against Tormach, but if your desire is to go less expensive you won't find it with features anywhere near as robust as Langmuir is offering. Just the spindle motor is a 3.4hp servo(!) 0-8000rpm with encoder. That right there puts it in a spindle class in the same ball park of Tormach's 1500MX. Which is crazy.
At current costs if I was starting all over again right now and my budget max was around $5k and no higher I'd jump on the Langmuir immediately.
If you can and will pay more, Tormach will probably be (for now) more polished, and much more long lasting machine under abuse (my opinion).
Smallest? Tormach PCNC 440, no enclosure, bolted to a bench is a crazy small footprint for what it can do. Many people swear by them, but I'm not personally fond of the 440's Z axis envelope, .75 horsepower, or it's different VFD control that doesn't do reverse the same as all their other mills. I'm a 770 guy myself. A PCNC 770M with no enclosure and no frills bolted to a workbench would be very small-ish and get you decent capability (1.5 hp, 10k RPM) in a small space. Check out the older videos from Craig's Machine Shop on Youtube. He shows what you can get done with it bolted to a heavy wood workbench. With any mill in your limited space I'd recommend a shower curtain type enclosure surrounding it from the ceiling down. Just push back the curtains around back to access everything and minimize space taken up by the machine. 600sq ft you don't have room for full solid enclosures... you'll end up unable to access anything on the sides or back making maintenance a nightmare.
However... The Langmuir MR-1 is quite a lot of machine for it's price. I've owned a Tormach 770 S3 for years but a friend was considering the Langmuir and I spent some time comparing specs with him. It looks very, very capable for a home shop. Maybe about perfect for a whole lot of people's needs considering the balance of price and performance. I have now seen a few videos of people doing runs of parts and it seems to do it quite well. Bear in mind that a gantry will expose your ballscrews and rails to tons of chips and swarf and Z height will be somewhat limited although the Langmuir is good for a gantry in that regard. I don't know how it will hold up to a lot of use it looks ok, but Tormach is proven in that regard.
Langmuir: Gantry design. Much more work area, more HP, half the price or less of even the cheapest Tormach. Exposed rails and screws. Quite a bit of DIY to get it assembled and going but looks exceptionally well documented and supported.
vs.
Tormach: Dovetail traditional mill design. MUCH more mature control and software, more optional accessories like tool changer and power drawbar, normal way covers and ball screws down underneath away from debris. Very easy to get it setup and start using it. They are not cheap and only the 440 and 770 can be purchased new under 10k with very frugal options.
Good luck on the hunt.